Nowadays, semiconductor devices having higher degrees of integration are in high demand. Thus, active research is being conducted on methods of forming a fine pattern having a line width equal to or less than 100 nm. The fine pattern may be formed through a photolithography process using a photoresist having photosensitive characteristics.
The photolithography process typically includes a step of forming a photoresist film, a step of aligning/exposing the photoresist film and a step of developing the photoresist film so as to form a photoresist pattern. In the step of forming the photoresist film, a photoresist, the molecular structure of which may be changed by light, is coated on a substrate to form the photoresist film. In the step of aligning/exposing the photoresist film, a mask having a circuit pattern is aligned on the photoresist film formed on the substrate. Thereafter, light having an image of the circuit pattern of the mask is irradiated onto the photoresist film to generate a photochemical reaction. Irradiation causes the molecular structure of the exposed portions of the photoresist film to selectively change. Thereafter, the photoresist film is developed to form the photoresist pattern on the substrate.
In the step of developing the photoresist film, the photoresist film exposed to light is selectively removed or remains to form the photoresist pattern having a shape corresponding to the circuit pattern. The resolution of the photoresist pattern may be represented by the following Formula 1.R=k1λ/NA (R: maximum resolution, λ: wavelength, k1: constant, NA: numerical aperture of a lens)  <Formula 1>
As the wavelength of the light used for the step of exposing is decreased, the resolution of the photoresist pattern is improved, and the line width of the photoresist pattern is reduced. Thus, the minimum possible wavelength of the light, an exposing device based on the wavelength, and the maximum resolution of the photoresist may be considered important in forming a fine pattern having a nanoscale resolution.
The photoresist may be classified as either a negative photoresist or a positive photoresist. In the case of the positive photoresist, a cured portion of the photoresist film depends on a separation reaction of a blocking group due to an acid generated by a photoacid generator. For example, the acid generated by the photoacid generator is used for separating a specific blocking group, which is combined with a resin of the photoresist film, from the resin. Thus, the resin, from which the blocking group is separated, is changed to be easily dissolved in a developing solution in the subsequent developing process.
When a photoresist for argon fluoride (ArF), which is used for forming a pattern having a line width equal to or less than 75 nm, is used for forming a pattern, a manufacturing margin of an iso-dense pattern may not be sufficient. An insufficient manufacturing margin of the iso-dense pattern may cause a substantial difference between an actual critical dimension and a desired critical dimension in a peripheral area where pattern density is low compared to a cell area. In order to prevent and/or to reduce the above-mentioned problems, the amount of a photoacid generator may be increased. However, the photoresist pattern may be damaged so that an upper portion of the photoresist pattern may have a round shape. Furthermore, the photoacid generator may have hydrophobic characteristics so that the photoacid generator is not easily mixed with the resin having hydrophilic characteristics. Thus, the photoacid generator may not be uniformly distributed.
For example, referring to FIG. 1, a photoacid generator 14 of a photoresist film 10 has different characteristics from a resin 12. Thus, the photoacid generator 14 is not found near the resin 12, and adheres to each other in an upper portion of the photoresist film 10. Thus, a path, through which an acid generated by the photoacid generator 14 diffuses, is increased so that a photoresist pattern formed from the photoresist film 10 may not have a uniform profile.